On Mon, Jun 03, 2002 at 11:16:35AM +0200, Seth Mos wrote:
> At 12:35 2-6-2002 -0700, Raymond wrote:
> >I have enabled write-backing caching on a MegaRAID 1500 with battery back-up.
> >
> >Two other cache options exist: Read-Ahead and I/O Caching.
> >
> >Any potential problems enabling these options with XFS 1.02?
>
> I have not found any using caching IO.
>
> Read ahead can safely be used, but the readahead under linux itself is
> probably more usefull.
More importantly, you don't *want* to use readahead because it will waste
valuable cache space on the controller that could be used to cache small
writes. Unless you have a truly silly memory configuration (e.g. more
cache RAM on the RAID controller than main memory available for buffer
cache on your machine) the read cache of the operating system will do all
that the controller's cache could do and then some. On the other hand,
since the controller has battery backup, it can do something the OS can't:
safely gather small writes into its battery-backed cache and clear them to
disk in an efficient manner. So if your RAID controller lets you configure
its cache that way, that's what you want to do.
Thor
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